372 CARBONIC ACID. 



vided it does not exceed one eighth of the whole ; beyond that it is 

 injurious. 



(v.) This gas exists in fermented liquids ; we may collect it from 

 any fermenting mixture, or from bottled cider, beer, porter, &LC. and 

 it will prove to be carbonic acid. 



(iv.) This may be shewn by drawing the cork under water the 

 mouth of the bottle being immersed, the gas, at least what is spon- 

 taneously disengaged, will collect at top, and the rest may be obtain- 

 ed by boiling the fluid in a proper gas apparatus. 



5. MISCELLANEOUS. 



(a.) Carbonic acid gas, on account of its gravity, is often found 

 at the bottom of wells and caverns, as in the grotto Del Cani, near 

 Naples, and thus often destroys those who incautiously descend into 

 them ; by letting down a candle, it may always be determined 

 whether the place is safe. 



(b.) Jls the combustion of charcoal, and other carbonaceous sub- 

 stances, always generates carbonic acid, it is unsafe ever to remain 

 in a confined situation, in such an atmosphere ; in both these modes 

 many lives are destroyed. When it is pure, it produces a spasm of 

 the glottis, and suffocation ensues ; if so much diluted as to pass in- 

 to the lungs, it operates as a narcotic poison.* 



(c.) There are many other gases evolved in combustion, and all 

 of them are deadly ; nitrogen is always present in such cases, and 

 frequently carburetted hydrogen, gaseous oxide of carbon, ammonia, 

 and various vapors, as of pyroligneous acid, &tc. 



(d.) Fire should, therefore, always be made under a good drawing 

 vent. 



(e.) Carbonic acid is eminently salutary in the stomach, although 

 fatal in the lungs ; witness the native and artificial acidulous waters ; 

 its action in the primae viae is that of a mild stimulant. With com- 

 mon air, it exists, dissolved, in all natural waters, and imparts to 

 them pungency ; hence the flatness of boiled water, or of that which 

 has been exposed to air pump exhaustion. 



(/.) Carbonic acid gas. is the principal agent in raising bread ; 

 it is generated in the fermenting mixtures, as yeast, the sediment of 

 beer,f &c., and the native or artificial acidulous waters will inflate 

 dough and make it light. 



(g.) Carbonic acid exists every where in the atmosphere ; it was 

 found on the top of Mount Blanc, by Saussure,J and aeronauts 

 have brought it down from the greatest heights to which man has as- 



* It is supposed by many, that charcoal, when burning without smoke, is harm- 

 less, and that the anthracite coal does not produce a noxious gas ; both these are very 

 dangerous popular errors ; the deadly carbonic acid gas is rapidly formed from both, 

 during the whole time that they are burning. 



t Called in this country emptyings. t Jour, de Phys. XVII, p. 202. 



